What is Ferro Silicon Calcium?
Ferro Silicon Calcium, also known as Calcium Silicon is a potent deoxidizer and desulfurizer utilized in the production of high grade steels. Although Silicon itself is a powerful deoxidizer, Calcium is by far more powerful. In addition, Calcium Silicon is used to control the shape, size and distribution of oxide and sulfide inclusions improving fluidity, machinability, ductility, and impact properties of the final product.
Calcium Silicon Uses
Because of the strong affinity between calcium and oxygen, sulfur, hydrogen, nitrogen and carbon in molten steel, the silicon calcium alloy is mainly used for deoxidizing, degaying and fixing sulfur in molten steel. The addition of si-ca to molten steel produces a strong exothermic effect. Calcium changes into calcium vapor in molten steel, which can stir the molten steel and is beneficial to the floating of non-metallic inclusions. After deoxidation of si-ca alloy, non-metallic inclusions with larger particles and easy floating are produced, and the shape and properties of non-metallic inclusions are changed.
Therefore, si-ca alloy is used to produce clean steel, high quality steel with low oxygen and sulfur content, and special steel with low oxygen and sulfur content.The addition of si-ca alloy can eliminate the nozzles in the ladle nozzle of steel with aluminum as final deoxidizer and the nozzles in the intermediate tank of continuous cast steel | iron making.In the outside refining technology of steel, the content of oxygen and sulfur in steel is reduced to a very low level by deoxidizing and desulfurizing with silica calcium powder or core wire.The sulfide form in steel can be controlled and the utilization rate of calcium can be improved.In the production of cast iron, si-ca alloy plays an inbreeding role in addition to deoxidation and purification, which is conducive to the formation of fine grains or spheroidal graphite.The distribution of graphite in gray cast iron is uniform and the tendency of white cast iron is reduced.And can increase silicon, desulfurization, improve the quality of cast iron
Calcium Silicon Production
Calcium silicon is produced in submerged arc electric furnaces from quartz, limestone and coal as raw materials. Calcium silicon for cleaning steel inclusion is considered one of the most practical ways to introduce calcium in the treatment, a stage at which the ferroalloy is in a liquid state.
Calcium is a powerful modifier of oxides and sulphides. It transforms alumina inclusion in complex calcium aluminate compounds thus improving the machinability of steel, increasing the life of cutting tools and decreasing the amount of energy present troughout the process, with the evident advantages that this involves.
It improves the castabilit of steel, with this being a very important fact in the continuous casting process by preventing the deposit of solid inclusions within the tundish nozzles, thereby preventing their obstruction.
Calcium Silicon is also utilized in combination with Barium. The Barium increases the density and reduces the vapor pressure of the alloy, thereby improving efficiency. In cast irons it is used mainly by Pipe Shops for the purpose of coating the inside of each mono cast machine.
Calcium Silicon can be obtained in lump or powder form. The most widely used method for integrated steel applications is in the form of cored wire. This is mainly because calcium has a low density and high reactivity in the ladle making it difficult to introduce and retain in the melt. Cored wire eliminates these variables.
Calcium Silicon Properties
| PHYSICAL STATE | Solid |
| COLOUR | Metallic gray |
| ODOUR | Odourless |
| MELTING POINT | 900-1000℃ |
| BOILING POINT | – |
| SPECIFIC GRAVITY | 2.5g/cm³ |
| MAIN CONTENT | Ca22-35%, Si60-65%, Fe<6% |
When in contact with moisture or water, it may release hydrogen and may form flammable or explosive mixtures with air. What is more, impurities can produce arsine ( identifiable by its garlic smell) and phosphine, developing toxic gases in such proportions that, under conditions of mechanical ventilation, the risk of poisoning clearly prevails over that of explosion. It occurs more abundantly in recently fragmented surfaces
Specification of Calcium Silicon
| roduct | %Ca | %Si | %Fe | %C | %S | %P | %Ti | %Al | %Ba |
| Calcium Silicon Lump | 28.0-32.0 | 60.0-65.0 | 7.0 Max | 1.0 Max | 0.07 Max | 0.05 Max | 0.20 Max | 1.50 Max | |
| Calcium Silicon Barium | 11 Min | 50 Min | .50 Max | 2.0 Max | 11 Min |
Calcium Silicon Production Method
There are several methods are reported in literature for the production of calcium silicon, there method are mainly based on use of different combinations of the following materials: 1.calcium carbide, silica and carbon. 2 calcium oxide, silica and carbon;3. calcium carbonate, silica, calcium fluride and calcium chloride; 4 silicon carbide, calcium carbide and quartz; 5. calcium oxide and an aluminium silicon alloy. And mostly methods for industrial method for the production of calcium silicon alloys are:
1. Calcium Carbide Method: the reduction of silica with carbon takes place in the presence of calcium carbides
2 SiO2 + 2 C+ CaC2 = (CaSi2) alloy + 4 CO
The standard Gibbs energy of this reaction is
ΔG0 = 14,24,558.7 – 792.97T， Joules/g mole
The theoretical initial temperature of reduction ( P∞ = 1 atm) is 1520℃
In this method calcium silicon is produced in a shaft type electric furnace, the charge mix consists of quartzite, calcium carbide and a mixture of coke with charcoal.
- Quick Lime Method: Calcium silicon is produced in a single stage, omitting the production of calcium carbide. In this method, production of calcium silicon is based upon the reduction by carbon of CaO and SiO2 according to the following reaction
- 2 SiO2 + CaO + 5 C = (CaSi2) alloy + 5 CO
The standard Gibbs energy of this reaction is
ΔG0 = 18,90,507.60 – 1,020.65 T， Joules/g mole
The theoretical initial temperature is about 1580℃
The smelting of calcium silicon according to this method requires a very precise proportioning of the charge. The least shortage of the reducing agent intensifies the formation of slag from CaO and SiO2, and when it is in excess, the depth of immersion of the electrodes into the charge is reduced very quickly. Causing an intensive evaporation of calcium and silicon and cooling of many parts of the furnace. This in turn causes the accumulation of carbides of calcium and silicon.
The quick lime method is preferred compared to the calcium carbide method since it is more efficient.